The present invention relates to multipotent stem cells (MSCs) purified from peripheral tissues including peripheral tissues containing sensory receptors such as skin, olfactory epithelium, mucosa, and tongue. The invention also relates to cells differentiated from these multipotent stem cells. The invention includes pharmaceutical compositions and uses of either the multipotent stem cells or the differentiated cells derived from such stem cells. Additionally, business methods based on the multipotent stem cells or the differentiated cells are contemplated.
There are a number of diseases of the central nervous system (“CNS”) which have a devastating effect on patients. These diseases are debilitating, often incurable, and include, for example, Alzheimer's disease, Huntington's disease, Parkinson's disease, and Multiple Sclerosis.
By way of example, Parkinson's disease is a progressive degenerative disorder of unknown cause. In healthy brain tissue, dopaminergic neurons extend from the substantia nigra of the brain into the neighboring striatum. In Parkinson's disease, these dopaminergic neurons die.
There are a number of methods to treat Parkinson's disease. One method is to treat humans having Parkinson's disease with L-DOPA. A second method is to transplant cells into the substantia nigra or striatum. Transplanted cells replace endogenous cells that are lost as a consequence of disease progression. An animal model of Parkinson's disease is an MPTP-treated non-human primate. The MPTP-treated animals have been transplanted with dopamine-rich embryonic neurons with some success.
To date, the cells used for neural transplant have been collected from the developing brains of aborted fetuses. Aside from the ethical considerations, the method from a practical standpoint is unlikely to provide a sufficient amount of neural tissue to meet the demands. Thus, another source of cells for transplantation is desirable.
Stem cells are undifferentiated cells that exist in many tissues of embryos and adult organisms. In embryos, blastocyst stem cells are the source of cells which differentiate to form the specialized tissues and organs of the developing fetus. In adults, specialized stem cells in individual tissues are the source of new cells, replacing cells lost through cell death due to natural attrition, disease, or injury. Stem cells may be used as substrates for producing healthy tissue where a disease, disorder, or abnormal physical state has destroyed or damaged normal tissue.
Weiss et al., 1996 summarizes the five defining characteristics of stem cells as the ability to:                Proliferate: Stem cells are capable of dividing to produce daughter cells.        Exhibit self-maintenance or renewal over the lifetime of the organism: Stem cells are capable of reproducing by dividing symmetrically or asymmetrically to produce new stem cells. Symmetric division occurs when one stem cell divides into two daughter stem cells. Asymmetric division occurs when one stem cell forms one new stem cell and one progenitor cell. Symmetric division is a source of renewal of stem cells. This permits stem cells to maintain a consistent level of stem cells in an embryo or adult mammal.        Generate large number of progeny: Stem cells may produce a large number of progeny through the transient amplification of a population of progenitor cells.        Retain their multilineage potential over time: Stem cells are the ultimate source of differentiated tissue cells, so they retain their ability to produce multiple types of progenitor cells, which will in turn develop into specialized tissue cells.        Generate new cells in response to injury or disease: This is essential in tissues which have a high turnover rate or which are more likely to be subject to injury or disease, such as the epithelium of blood cells.        
Thus, the key features of stem cells are that they are multipotential cells which are capable of long-term self-renewal over the lifetime of a mammal.
MSCs may be used as a source of cells for transplantation. The stem cells may themselves be transplanted or, alternatively, they may be induced to produce differentiated cells (e.g., neurons, oligodendrocytes, Schwann cells, or astrocytes) for transplantation. Transplanted stem cells may also be used to express therapeutic molecules, such as growth factors, cytokines, anti-apoptotic proteins, and the like. Thus, stem cells are a potential source of cells for alternative treatments of diseases involving loss of cells or tissues.
The safest type of tissue graft (using stem cells or otherwise) is one that comes from self (an autologous tissue source). Autologous tissue sources are widely used in procedures such as bone transplants and skin transplants because a source of healthy tissue is readily accessible for transplant to a damaged tissue site. In brain diseases, such as Parkinson's disease, healthy dopaminergic neuronal brain tissue may exist at other sites in the brain, but attempts to transplant these neurons may harm the site where the healthy neurons originate. Multipotent stem cells that can be differentiated into dopaminergic neurons may be available at other sites from which they may be transplanted, but the CNS, particularly the brain, is physically difficult to access.
In several tissues, stem cells have been purified and characterized. For example, neural stem cells have been purified from the mammalian forebrain (Reynolds and Weiss, Science 255:1707-1710, 1992) and these cells were shown to be capable of differentiating into neurons, astrocytes, and oligodendrocytes. PCT publications WO 93/01275, WO 94/16718, WO 94/10292 and WO 94/09119 describe uses for these cells. It could be impractical or impossible, however, to first access brain or other CNS tissue for biopsy and then again for transplant in patients with weakened health. It would be very useful if there were accessible stem cells capable of differentiating into CNS cell types, such as dopaminergic neurons; such cells would be a source of cells for autologous transplants.
Thus, there is a clear need to develop methods for identifying from accessible tissues multipotent stem cells that can act as a source of cells that are transplantable to the CNS, PNS, or other tissues in vivo in order to replace damaged or diseased tissue.